1. Field of the Invention
The present invention relates to a device for preventing eavesdropping through a speaker, and more particularly, to a device for preventing eavesdropping, which transmits a jamming signal through a speaker common signal line.
2. Discussion of Related Art
The development of electronic devices has provided society with added convenience, but has also led to growing problems such as leakage of private information. Today, invasion of privacy and violation of individuals' rights by means of various types of electronic devices have become serious social problems.
For example, a speaker is generally used to output sound, but it can sometimes be operated as a microphone and misused as a means for eavesdropping.
FIGS. 1A and 1B are schematic diagrams illustrating structures of a speaker and a microphone.
Referring to FIG. 1A, a speaker includes a coil 102 surrounding a permanent magnet 101 and speaker cone 103 attached to the coil, which generates sound due to vibration of the speaker cone 103 caused by an electromagnetic force in accordance to the Lorentz force law when an output current of an electrical signal generator 104 flows through the coil 102.
Referring to FIG. 1B, a microphone, which is the same as the speaker, includes a coil 106 surrounding a permanent magnet 105 and speaker cone 107 attached to the coil. However, unlike the speaker, the microphone can receive sound information at an electrical signal receiver 108 by applying a current through the coil 106 due to electromagnetic induction when the speaker cone 107 is vibrated by external sound.
As described above, since the speaker and microphone are basically formed with the same structure, a current can also be induced to a coil in the speaker by external sound like in the microphone. Moreover, in the case of a speaker used for broadcasting in a building, a plurality of which are installed on the ceilings and walls of rooms while connected with a common signal, an electrical signal induced from the speaker is transmitted through a speaker common signal line. An eavesdropper is then able to receive the induced electrical signal through a speaker common signal line, thereby eavesdropping on any conversations made in the room where the speaker has been installed.